Method of making hard compositions



Feb. 6, 1940. w. A. .WISSLER METHOD OF MAKING HARD COMPOSITIONS FiledMarch 5, 1938 INVENTOR WILLIAM A.WISSLER ATTORNEY METHOD OF HARDCOMPOSITION? William A. Wissler, Niagara Falls, N. Y., assignor toHaynes Stellite Company, a corporation of Indiana Application March 5,

1 Claim.

This invention relates to the production of cast hard compounds ofdiflicultly fusible metals, and compositions containing such compounds.

To produce hard, strong casings of the carbides 5 or other hardcompounds of difl'icultly fusible metals, or of alloys containing suchcompounds, mixtures of the desired ingredients are ordinarily melted andthe fused products rapidly solidified in molds and rapidly cooleddirectly after their solidification. The methods of melting and coolingheretofore in use involve the melting of small individual batches ofcompound, or the constituents thereof, in a crucible. The extremely hightemperature required to melt the compounds limits the amount of materialthat can expediently be melted in any one batch by these methods andalso causes excessive burning or scoring of the molds and crucibles.Ordinarily, a mold or crucible can be used only once, or at most only afew times. Further, such molds and crucibles usually consist of carbonand at the high temperatures involved the melt tends to pick up asubstantial proportion of this element. Inasmuch as the carbon contentof the cast hard compound must be within certain well defined limits toobtain a material of optimum physical properties much of the castcompound produced by the methods heretofore in use is oftenunsatisfactory.

An object of this invention is to provide a continuous orsemi-continuous process, free from the disadvantages mentioned above,for the production of cast carbides, borides, silicides, nitrides, andother hard compounds, of the diflicultly fusible metals of the fourth,fifth, and sixth groups of the Mendelejeif periodic arrangement of theelements, with or without auxiliary metals such as iron, cobalt, andnickel. Another object is to provide apparatus suitable for use inpracticing the process of the invention- A further object is to providecast compounds of the class defined above in the form of elongatedpellets.

These and other objects are attained in the process of the presentinvention which comprises preparing bonded mixtures of the desiredingredients and melting and cooling said mixtures in the mannerexplained below.

The invention will be described in connection with the attached drawing,in which:

Fig. 1 is a sectional schematic view of a form of an apparatus embodyingthe invention; and

Figs. 2 and 3 are sectional schematic views of alternative forms of theapparatus shown in Fig. 1.

In the production of cast hard compounds by a continuous process of theinvention employing 1938, Serial No. 194,109 (01. -137) the form of theapparatus shown in Fig. 1, a mix 21, consisting of the desiredingredients, suitably in comminuted form, in the desired proportionstogether with a carbonaceous binder such as pitch, glue, or oil, orother binder, is placed in a mixing chamber 24 which suitably comprisesa continuous screw 25, a die 23 having a plurality of small holes, and asecond die 26 having a single opening preferably centrally located. Thechamber 24 may, if desired be heated, in any suitable manner, to lowerthe viscosity of the bonding materials of the mix, thus ensuring a moreintimate mixture between the comminuted dry ingredients and the bondingmaterials. The bonded mix 2! essentially contains at least one of thediflicultly fusible metals of the fourth, fifth, and sixth groups of theperiodic system, for example, chromium, molybdenum, tungsten, titanium,zirconium, vanadium, columbium, or tantalum, or compounds of suchmetals, and at least one of the hard compound forming elements such ascarbon, boron, or silicon, or nitrogen, or compounds of said elements,with or without one or more auxiliary metals such as iron, cobalt, andnickel.

The bonded mix 21 is forced, by means of thescrew 25, through the die 23and the die 26 into and through a baking furnace 22, from which itemerges as a solid coherent mass or rod II. The baking furnace is heatedby an electric resistance 28 or by other appropriate means.

' The rod H is connected as one electrode in an electrical circuit, andan electrode I2, preferably of carbon or graphite, is connected as theother electrode. Inasmuch as the process is continuous, the electricalconnection may be made to the rod II by suitable contact with the mix 21at a point near the baking furnace 22. Preferably, the rod II is madethe positive electrode, and the carbon I 2 the negative electrode, butthe polarity of the two electrodes may be reversed or an alternatingcurrent may be substituted for a direct current. The electrode l2 may beheld by an electrode holding and feeding device M of any desired type toestablish and maintain an electric are H] of constant length and ofsufficient intensity to melt 'the electrode H. A cover l5 may beprovided, if desired containing openings for the insertion of theelectrodes and for the insertion of a tube 20 through which an inert orreducing gas, such as hydrogen or nitrogen, may be introduced. The coverI5 preferably consists of a non-conducting material; if the cover is aconducting material, it should be insulated from the electrode. Thecover l5 and the electrode holding and feeding device M are supported ona platform 16 provided with an' opening I! through which compound meltedby the heat of the arc ID, in the form of individual elongated pelletsi9, is discharged by gravity into a receptacle l8 located under theopening I! and containing a quenching medium 2| such as oil, water, gas,or molten salt. The pellets l9 do not agglomerate or cohere, and theymaybe removed from the quenching medium without interrupting the meltingoperation. If-desired, the pellets of cast compound may be cooled byother means, for example, by air cooling or by permitting the compoundto remain in close proximity to a colder solid body.

In the production of cast hard compounds employing the alternative formof apparatus shown in Fig. 2, the rod II is prepared independently ofthe melting operation, and is melted in the simplified apparatus shown.The various parts of the apparatus of Fig. 2 are designated by numeralscorresponding to those of Fig. 1 so that the description of meltingandquenching given in connection with Fig. 1 applies, in a like manner, toFig. 2.

In the production of cast hard compounds employing the form of theapparatus shown in Fig. 3, the rod II, which may be prepared either asdescribed in connection with Fig. l or independently of the melting andquenching operations, is melted by the heat of an electric are formedbetween carbonaceous electrodes I2. The method of quenching the meltedcompound is the same as that described in connection with Fig. 1. Theform of the apparatus shown in Fig. 3 is especially applicable to themelting of bonded rods which are substantially non-conducting, forexample, rods bonded with soluble silicate bonding materials such assodium silicate.

Alternatively a conductive composite rod similar in composition to herod ll may be substituted for the carbp electrode l2 in any of the formsof the apparatus and process described above.

A typical procedure for the production of cast tungsten carbide,employing the form of apparatus shown in Fig. 2, is as follows:

A pulverized mixture consisting of: Tungsten carbide (2.58% C.) 1 gm2400 Cobalt gm 24 Carbon gm 12 Pitch gm 184 Oil cc 40 was heated andformed into a plastic mass and extruded, while hot, intoa composite rodfivesixteenths of an inch in diameter. The rod was then baked to convertthe pitch into coke and to form a solidly cohering mass. An arc wasformed between the composite rod connected as the positive electrode,and a graphite rod connected as the negative electrode, in a directcurrent circuit. A currentofabout 200 to 250 amperes was used. As thecomposite metal rod melted, the molten material, in the form ofindividual elongated drops or pellets, was immeamass? diately dischargedby gravity into a receptacle containing water. A chemical analysis 01'the cast tungsten carbide and cobalt composition so produced revealedthat it contained 3.6% carbon, which is approximately the carbon contentrequired for optimum physical properties in a cast hard compound of thistype. Furthermore,

of illustration, and the present invention is not limited to or by suchexamples. Although I have described the production of cast tungstencarbide alloy as an example, it is within the invention to producecarbides, borides, silicides, nitrides, or other hard compounds of anyof the difiicultly fusible metals such as chromium, molybdenum,tungsten, vanadium, columbium,

tantalum, titanium, or zirconium, or alloys containing such hardcompounds.

By the method of the present invention, crucibles, molds, and otherexpensive refractories heretofore used in the production of cast hardcompounds are eliminated. Also, the recovery of cast compound inrelation to the amount of composite rod melted is comparatively high.Further, the carbon content of the compound may readily be held withinthe narrow composition limits necessary to produce a cast hard compoundof optimum physical properties. The method of the present invention maybe made either continuous or semi-continuous, thus permitting greaterflexibility in the production of cast hard compounds than heretoforeavailable.

Cast hard compounds produced in accordance with the invention areordinarily in the form of elongated pellets which are substantiallyhomogeneous in structure and composition. Such pellets are suitable foruse as hard facing material for tools, or in other applications wherehigh resistance to wear and abrasion is one of the requisites of thematerial. They may readily be applied to metal surfaces by welding,either electric or oxy-acetylene, or by any other well known methods. Ifdesired, the pellets may be enclosed in a metal sheath, or bonded with asuitable binder, and advantageously employed in this manner as hardfacing welding rods.

I claim:

A method of producing cast compositions of the class described whichcomprises mixing the ingredients thereof with a binder; forming saidbonded mixture into a solid rod; melting said rod by the heat of anelectric arc formed between said rod and a carbonaceous electrode, andpromptly discharging the fused composition by gravity'into a coolingmedium.

- WILLIAM A. WISSLER.

